Integrated circuits have evolved into complex devices that include multiple levels of metal layers to electrically interconnect discrete layers of semiconductor devices on a single semiconductor chip. Recently, with the evolution of higher integration and higher density of integrated circuit components, the demand for greater speed of the data transfer rate is required. For this reason, an insulating film having high compressive stress, low leakage current, low dielectric constant to give the small RC delay is employed.
As the device dimensions continuously shrink, the RC time delay of the interconnect system becomes one of the most important limitation factors to the integrated circuits performance. The RC delay is directly proportional to the resistivity of the metal and the dielectric constant of the dielectric. In order to minimize the signal propagation delay, it is inevitable to use low dielectric constant materials as the inter-layer and intra-layer dielectrics (ILD). While many low-k (k<3.0) materials have been used as ILDs, silicon nitride with a high dielectric constant (k>7.0) is still the primary candidate for the Etch Stop Layer (ESL) required in copper damascene structures. Thus, it is desirable to replace silicon nitride by new materials with lower dielectric constants to further reduce the effective dielectric constant of the Cu interconnect system. In recent years, increasing interest has been focused on the study of high stress and thermally stable low-k silicon carbide based films deposited by PECVD using organosilicon gases.
Furthermore, to reduce the size of interconnection lines and vias is to change the wiring materials from the conventional aluminum (Al) to copper (Cu) wiring having low electric resistance.
However, to produce a semiconductor device having multi-layered copper wiring, a low dielectric constant insulating layer is formed as the interlayer insulating film on the copper wiring.
The use of copper as the interconnect material has various problems. For example, copper is easily diffused into the low dielectric constant insulating film from the copper wiring, thus increasing the leakage current between the upper and lower wiring.
The use of silicon carbide films as copper diffusion barrier layers has been published in U.S. Pat. No. 5,800,878. The dielectric constant of this film is about 5, and in addition it is used as copper diffusion barrier layers for 130 nm-nodes Large Scale Integration (LSI) technologies where the dielectric constant of the interlayer dielectric film is 3.
For next generation, 100 nm/65 nm-nodes Ultra Large Scale Integration (ULSI) technologies, the reduction of interconnect capacitance is important for suppressing the signal delay as well as the power consumption. Interlayer dielectric films with dielectric constant less than 2.5 are used with copper damascene structures. To decrease the effective dielectric of fine pitched lines, further reduction in the dielectric constant is necessary not only for the inter layer dielectric film itself but also the supporting dielectric films such as hard mask, etch stop layers and copper diffusion barrier layers.
The interface between copper and copper diffusion barrier layer is known to be the key point for the electro-migration reliability of copper interconnects. The interface between copper and the copper diffusion barrier layer is the dominant diffusion path. However, there is no report on the identification of the dominant path for copper interconnects. On the other hand, the interface can be not only the dominant path but also the electro-migration induced void nucleation site.
The strength of adhesion between copper and diffusion layer would affect the electro-migration induced void nucleation because electro-migration induced void nucleates when copper atom at the interface is stripped away from the diffusion layer. Films with high compressive stress provide better adhesion with copper. It is also suggested that in order to prevent the migration of metal atoms, the film has to have high compressive stress such as above 200 MPa where the stress is stable even after being directly exposed to air at room temperature of about 20 to 30° C. Furthermore, the leakage current and dielectric constant of such film at 1 MV/cm has to be less than that of 1×10−8 A/cm2 and less than 5.0 respectively. SiCN films with dielectric constant less than 5 such that the leakage current at 1 MV/cm is less than 1×10−8 A/cm2 are suggested to be suitable to substitute for such films.
Using the silicon carbide film as an etch stop film was developed and presented in U.S. Pat. No. 5,800,878. A dielectric constant of the silicon carbide film is approximately 5. Silicon carbide films are applied to LSI devices using copper wiring in combination with carbon-containing silicon oxide films, whose dielectric constant is approximately 3. There are several different types of compositions for what is generally called silicon carbide films. One type is a silicon carbide film comprising Si, C and H. This film's stress and dielectric constant change if it is left in the atmosphere. This is due to the oxidation of the top surface of the silicon carbide film. The method to minimize the oxidation of carbon containing materials, such as silicon carbide, with an inert gas plasma such as helium (He), Argon (Ar) is published in JP laid-open patent 2001/0060584. This inert gas plasma treatment only minimizes the top surface of the silicon carbide film from getting oxidized, however, no changes/improvements to the film properties are observed.
The method of forming nitrogen doped silicon carbide (SiCN), oxygen doped silicon carbides (SiCO) has been published in U.S. Patent Application Publication 2001/0030369, U.S. Patent Application Publication 2002/0027286, U.S. Patent Application Publication 2001/0051445, and U.S. Patent Application Publication 2001/0031563. Furthermore; these films have been proposed as copper diffusion barrier layers. Though a silicon carbonitride layer has been proposed as a copper diffusion barrier layer with low leakage current, its dielectric constant is high and film stress is less compressive such as 5.5 and 100 MPa respectively.
In case of oxygen doped silicon carbide, although its dielectric constant is relatively low, such as less than 5, it cannot sufficiently refrain from increasing the leakage current. To decrease the leakage current to a sufficient level, the oxygen must be introduced much more into the silicon carbide film.
However, to do so, the leakage current can be reduced up to a satisfactory level, nevertheless a new problem is caused such that the surface of the copper wiring is oxidized and thus the barrier insulating film and the inter dielectric layer is ready to peel.